Carbon rod for electric-arc lamps.



UNTTED STATES PATENT OFFICE.

HUGO BREMER, OF NEHEIM, GERMANY.

CARBON ROD FOR ELECTRIC-ARC LAMPS.

SPECIFICATION forming part of Letters Patent No. 658,423, dated September 25, 1900. Application filed August 5, 1899. Serial No. 726,344. (No specimens.)

To (tZZ whom it may concern.-

Be it known that 1, HUGO BREMER, a subject of the Emperor of Germany, residing at Neheim-on-the-Ruhr, Germany, have invented certain new and useful Improvements in Carbon Rods for Electric-Arc Lamps, of which the following is a full and exact specification.

Among the many attempts which have been made for prolonging the duration of carbon electrodes is the coating with a metal or salt, such as borax or an alkali silicate, in order to prevent the disintegration of the heated common carbon by contact with the atmosphere. Such a process has bee described, for instance, in Roubals patent, 0. 559,7 52, and Brushs patent, No. 10,544. On the other hand, the luminosity of carbon electrodes has been increased by mixing them with salts of calcium, magnesium, strontium, or other suitable metals; but unless these admixtures are selected in a special manner or used in very small quan titysuch electrodes suffer from the defect that they produce slag which, accumulating near the crater, obscures the same and finally chokes the are. As far as I am aware the largest quantity of mineral matter that has ever been proposed is ten per cent. of the carbon mixture, and in practice not more than three per cent. has been used.

This invention relates to that kind of carbon electrodes for electric-arc lamps in which the carbon is uniformly mixed with luminiferous mineral matter, preferably salts of alkaline earths, which during the burning of the carbon produce a difficultly-fusible slag and which electrodes have a fusible coating adapted to protect the electrodes from contact with air, excepting at the extreme illuminating end, where the coating melts under the temperature of the voltaic arc.

The invention consists in a special combination of materials constituting the carbon mixture or body of the electrode on the one hand and the glassy coating on the other hand. I select the material for the coating in such a manner that it serves a double purpose, viz: first, to protect the surface of the carbon from atmospheric disintegration, and, secondly, to combine chemically and physically with the slag formed by the burning of the-carbon, so

:as to form a liquid which falls off easily in drops. This is the case if the coating consists of bora'cic acid or of an acid borate -for instance, borax-which salts when fused by the heat of the voltaic arc will combine with the basic slag-such as lime, magnesia, or strontia-tl1ereby forming a borate of lime or other alkaline earths,whioh fall oif in drops. I wish, however, to include neutral borates and acid or neutral silicates, which are known to act as a flux capable of absorbing, when in a fused condition, alkaline earths and other bases. If the glassy coating consists of an alkali silicate, it will when fused by the heat of the arc and brought in contact with theslag form a double silicate of lime, magnesia, or other base, which falls off in drops. The coating may be applied to the carbon electrode by known processes; but preferably by heating the otherwise finished electrode to red heat and then dipping it into a liquid consisting of fused boric acid or a borate or silicate, so that when taken out of the bath the carbon will have a glassy coating. During the burning of such electrodes in an arclamp the lower end of the positive carbon will become highly incandescent after a sufficient part of the coating has been removed to establish contact and to close the electric circuit. The glassy coating will melt for a height of about fifteen millimeters and will be caused to boil; but on account of its coherent nature or viscosity will not drop ofi. It flows around the lower parts of the electrode andevaporates only at the very hottest part, about one and one-half to two millimeters from the lower edge of the electrode. On the whole extent of the remaining surface the electrode will remain closed air-tight, so as to completely avoid the incineration of the carbon. The slag produced by the lime or other metallic base contained in the electrode forms short hard leaflets at the edge of the electrode; but it may be seen from time to time the molten coating reaches the said leaflets or scales, dissolves or mixes with them, and draws them up into the boiling mass if it has not previously dropped in small and innocuous particles.

The boiling mass surrounding the electrodes is rendered heavier by the absorption of the lime or other base and occasionally gives on. drops.

What I claim is- 1. A carbon electrode for arcdamps conslag produced by the burning of the electrode, substantially as described and for the purpose specified.

3. A carbon electrode for arc-lamps containing a salt of an alkaline earth uniformly mixed with the carbon and provided with a coating of a fusible material adapted to melt at the extremity of the electrode and then to absorb and chemically combine with the basic slag produced by the burning of the electrode; substantially as described, and for the purpose specified.

In witness whereof I have hereunto set my hand in the presence of two subscribing witnesses. I

I HUGO BREMER. Witnesses:

HENRY HASPER, WOLDEMAR HAUPT. 

